Devices of this type are disclosed in U.S. Pat. No. 3,083,961 and are used for partially automating processes in the apparel manufacturing industry. In the apparel manufacturing industry, automation is very important because this industry is still very wage-intensive as compared to other manufacturing industries. Automation is indispensable in view of the increasing cost pressure.
As is explained in the literature reference "Bekleidung-und-Maschenware" 22 (1983) No. 1, pages 6 to 11, considerable difficulties arise in restacking cloth parts, lifting such cloth planar work pieces perfectly from a work piece stack, and redepositing them in a stack at a prescribed position for further processing. If pneumatic pickup devices are used, only planar textile work pieces having a sufficiently small air permeability can be picked up and transported properly. Preferred prior art pickup devices operate according to mechanical principles using gripping systems which are equipped with pickup needles or clamping devices. However, as practice shows, such gripping systems have relatively low reliability and cannot be adapted optimally in every case to the greatly differing material properties of such planar work pieces.
Prior art pickups operating according to adhesive operating principles also have problems. Here, different material properties of work pieces do not play a large role. However, the adhesive force declines with use and in addition the adhesive surfaces become dirty. For this reason, as a practical matter, adhesive tape pickup arrangements can be only used wherein the apparatus includes adhesive-tape winding devices so that the adhesion surfaces can be continuously renewed during the course of the operating processes. The adhesive-tape pickup arrangement disclosed in U.S. Pat. No. 3,083,961 shows that such a pickup is a relatively bulky and complicated structure which permits practically no adaptation to work pieces having different dimensions. In the industry of apparel manufacture, however, great flexibility is demanded in such pickup devices because the cloth work pieces can differ very greatly as to size and also as to the dimensions.